1. Field of the Invention
This invention relates generally to conductive polymers and in particular to an anthraquinone-2-sulfonic acid doped conductive polymer formed on a textile material by chemical oxidation.
2. Prior Art
Electrically conductive textile materials and process for making the same are disclosed in Kuhn et al., U.S. Pat. No. 4,803,096. A textile material is contacted with an aqueous solution of an oxidatively polymerizable pyrrole or aniline compound, an oxidizing agent and a counter ion (doping agent). The pyrrole or aniline compound is oxidized and adsorbed on to the surface of the textile material to form a conductive polymer film. A variety of suitable doping agents are disclosed in the patent, preferably aromatic sulfonic acids such as benzene sulfonic acid and naphthalenedisulfonic acid. Modifications of the foregoing process designed to control the reaction rate by using a ferric salt as an oxidizing agent along with a weak complexing agent for ferric ions, and by using a vanadyl compound as an oxidizing agent are disclosed in Kuhn et al., U.S. Pat. No 4,877,646, and Kuhn et al., U.S. Pat. No. 4,981,718, respectively. One of the drawbacks of the above listed processes is that a relatively high concentration of dopant or counter ion must be present in the aqueous reaction solution in order to achieve high levels of conductivity in the polymer coated fabric.
In addition to chemical oxidation, pyrrole may be electrochemically oxidized to form conductive polypyrole. The effects of various dopants on the conductivity of electrochemically oxidized polypyrole has been the focus of research efforts. Kuwabata et al., EFFECT OF ORGANIC DOPANTS ON ELECTRICAL CONDUCTIVITY OF POLYPYRROLE FILMS, Synthetic Metals, Vol. 18, pp. 101-104 (1987). Kuwataba et al. found that film conductivity is higher for a dopant having a smaller number of sulfonate groups, i.e. anthraquinone-2-sulfonate and naphthalene-2-sulfonate. In a subsequent paper, Kuwataba et al. compared conductivity of the polypyrole films at various current densities used during film preparation. CONDUCTIVITY OF POLYPYROLE FILMS DOPED WITH AROMATIC SULPHONATE DERIVATIVES, J. Chem. Soc., Farraday Trans., Vol. 84(7), pp.2317-2326 (1988). Anthraquinone-2-sulphonate and anthraquinone-2,6-disulfonate were used as dopants with good results, especially at low current densities. Little, if any, difference was found between the various aromatic sulphonate dopants when higher current densities were used in film preparation. Further, the use of anthraquinone sulfonate to dope polyprole prepared by electrochemical oxidation is disclosed in Foos, U.S. Pat. No. 4,933,394 (col. 4, line 28-38). However, the behavior of polypyrole prepared by chemical oxidation, especially with regard to the conductivity and stability achieved using a particular dopant, does not parallel that of electrochemically oxidized polypyrole.